Arsenic is a widespread toxic environmental contaminant. Arsenic is fetotoxic and teratogenic when injected in animals, and recent reports have suggested arsenic as an etiologic factor in human birth defects. Thus, studies will be made in order to gain a better understanding of arsenic's prenatal effects. Effects of oral intake of arsenite during pregnancy will be evaluated by standard teratological techniques in two species (mouse and hamster). Additional dams will be allowed to litter, and their pups will be observed for 28 days to assess postnatal growth, behavior and survival. Methylated arsenic metabolites will also be tested for teratogenicity, to learn more about the role of arsenic metabolism in protection of the conceptus. Because chronic exposure to arsenic has been reported to lead to tolerance of the element's toxic effects, pregnant mice and hamsters will be treated with low levels of arsenite or of arsenate prior to a potentially teratogemic dose. The likelihood of a protective effect on the conceptus as a result of prior chronic exposure to arsenic can then be evaluated. In order to learn more of the mechanisms of arsenic's prenatal effects and about arsenic metabolism and to allow a correlation of the animal data with what is known of human metabolism, animals will be treated similarly to those in the aforementioned studies. They will be sacrificed following treatment, and uptake of arsenite, arsenate, and their metabolites by the conceptus and excretion by the mother will be determined. Arsenic and metabolite speciation will be assayed by atomic absorption spectrophotometric and GLC procedures. An additional study with mice will determine if BAL, given following, concurrent with, or prior to arsenite, can protect against prenatal effects.